Configuring Auto-MDIX

Prerequisites for Auto-MDIX

To configure Layer 2 parameters, if the interface is in Layer 3 mode, you must enter the switchport interface configuration command without any parameters to put the interface into Layer 2 mode. This shuts down the interface and then re-enables it, which might generate messages on the device to which the interface is connected. When you put an interface that is in Layer 3 mode into Layer 2 mode, the previous configuration information related to the affected interface might be lost, and the interface is returned to its default configuration.

Automatic medium-dependent interface crossover (auto-MDIX) is enabled by default. When you enable auto-MDIX, you must also set the interface speed and duplex to auto so that the feature operates correctly.

Auto-MDIX is supported on all 10/100/1000-Mb/s and on 10/100/1000BASE-TX small form-factor pluggable (SFP)-module interfaces. It is not supported on 1000BASE-SX or -LX SFP module interfaces.

Restrictions for
Auto-MDIX

The
switch
might not support a pre-standard powered device—such as Cisco IP phones and
access points that do not fully support IEEE 802.3af—if that powered device is
connected to the
switch
through a crossover cable. This is regardless of whether auto-MIDX is enabled
on the switch port.

Information about Configuring Auto-MDIX

Auto-MDIX on an
Interface

When automatic
medium-dependent interface crossover (auto-MDIX) is enabled on an interface,
the interface automatically detects the required cable connection type
(straight through or crossover) and configures the connection appropriately.
When connecting
switches without the auto-MDIX feature, you must
use straight-through cables to connect to devices such as servers,
workstations, or routers and crossover cables to connect to other
switches
or repeaters. With auto-MDIX enabled, you can use either type of cable to
connect to other devices, and the interface automatically corrects for any
incorrect cabling. For more information about cabling requirements, see the
hardware installation guide.

This table shows
the link states that result from auto-MDIX settings and correct and incorrect
cabling.

Table 1 Link Conditions
and Auto-MDIX Settings

Local Side
Auto-MDIX

Remote Side
Auto-MDIX

With Correct
Cabling

With Incorrect
Cabling

On

On

Link up

Link up

On

Off

Link up

Link up

Off

On

Link up

Link up

Off

Off

Link up

Link down

How to Configure Auto-MDIX

Configuring
Auto-MDIX on an Interface

SUMMARY STEPS

1.enable

2.configure terminal

3.interfaceinterface-id

4.speed
auto

5.duplex
auto

6.mdix auto

7.end

8.copy running-config
startup-config

DETAILED STEPS

Command or Action

Purpose

Step 1

enable

Example:

Switch> enable

Enables
privileged EXEC mode. Enter your password if prompted.

Step 2

configure terminal

Example:

Switch# configure terminal

Enters global
configuration mode

Step 3

interfaceinterface-id

Example:

Switch(config)# interface gigabitethernet1/0/1

Specifies the
physical interface to be configured, and enter interface configuration mode.

Step 4

speed
auto

Example:

Switch(config-if)# speed auto

Configures the
interface to autonegotiate speed with the connected device.

Step 5

duplex
auto

Example:

Switch(config-if)# duplex auto

Configures the
interface to autonegotiate duplex mode with the connected device.

Step 6

mdix auto

Example:

Switch(config-if)# mdix auto

Enables
auto-MDIX on the interface.

Step 7

end

Example:

Switch(config-if)# end

Returns to
privileged EXEC mode.

Step 8

copy running-config
startup-config

Example:

Switch# copy running-config startup-config

(Optional) Saves your entries
in the configuration file.

Monitoring Auto-MDIX

Command

Purpose

show controllers ethernet-controllerinterface-idphy

Verifies the operational state of the auto-MDIX feature on the interface.

Technical
Assistance

Description

Link

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